Research hotpots and frontier trends of neuroprotective effects of magnesium from 1999 to 2023: A bibliometric analysis

Abstract Background The neuroprotective effect of magnesium has been widely discussed, and its effectiveness has been confirmed by animal and clinical trials. However, there are still difficulties in clinical translation in diseases such as cerebral ischemia and subarachnoid hemorrhage. Therefore, it is necessary to analyze the literatures about neuroprotection of magnesium to reveal a more comprehensive knowledge framework, research hotspots and trends in the future. Methods Original articles and reviews related to neuroprotective effects of magnesium from 1999 to 2022 were retrieved from the Web of Science Core Collection (WoSCC). The bibliometrics CiteSpace 6.2.R4 software was used to conduct co‐occurrence/co‐citation network analysis and plot knowledge visualization maps. Results A total of 762 articles from 216 institutions in 64 countries were included in this study. The United States had the largest number of publications, followed by China and Canada. The University of California, UDICE‐French Research Universities, and the University of Adelaide were the top three institutions in publication volume. Crowther Caroline A was the most published and cited author. Among the top 10 cited articles, there were seven articles on neuroprotection in preterm infants and three on acute stroke. Keyword cluster analysis obtained 11 clusters, showing that current research hotspots focused on magnesium therapy in neurovascular diseases such as cerebral ischemia, spinal cord injury, subarachnoid hemorrhage, and emerging treatment strategies. Conclusion The neuroprotective effects of magnesium in preterm infants have been extensively studied and adequately confirmed. The therapeutic effects of magnesium on cerebral ischemia and subarachnoid hemorrhage have been demonstrated in animal models. However, the results of clinical studies were not satisfactory, and exploring new therapeutic strategies may be the solution. Recently, the combination of magnesium and hypothermia had great potential in neuroprotective therapy and may become a development trend and hotspot in the future.


| INTRODUC TI ON
3][4] Magnesium is distributed about half in bones, half in muscles and other soft tissues, and less than 1% in the blood. 58][9] Experimental evidence suggests that magnesium plays a protective role in a variety of neurological disorders, including headache, stress, acute brain injury, stroke, epilepsy, Parkinson's disease, and Alzheimer's disease. 10gnesium exhibits neuroprotective effects through both neuronal and vascular mechanisms.Magnesium is an endogenous antagonist of voltage-and ligand-gated calcium channels glutamate-N-methyl-D-aspartate (NMDA) receptor, which can reduce excitotoxicity caused by calcium overload after nervous system injury and reduce brain cell death. 11,12At the same time, magnesium is an important cofactor in energy production process of tricarboxylic acid cycle-oxidative phosphorylation reaction, which can maintain mitochondrial function and improve energy imbalance after brain injury. 12,13Magnesium can also regulate intracellular calcium levels in vascular smooth cells by inhibiting calcium channels. 14It reduces the production of endothelin-1 and inhibits the activation of myosin light chain kinase, thereby attenuating vasospasm and contraction and improving cerebral blood flow. 15In addition, studies have shown that magnesium can play a neuroprotective role by regulating blood-brain barrier permeability and reducing inflammatory response. 16,17Clinical experiments have demonstrated the neuroprotective efficacy of magnesium in preterm delivery and neonatal hypoxic encephalopathy.Studies on animals have also revealed that magnesium has neuroprotective properties in stroke.However, there are still difficulties in clinical translation in cerebral ischemia, subarachnoid hemorrhage, and other diseases.Therefore, it is necessary to conduct a literature analysis, identify the reasons that hinder its translation, and discover further research trends and hotspots.
In this study, CiteSpace, an information visualization software developed by Professor Chaomei Chen using Java language, 18 was used to objectively analyze the characteristics of the literatures on magnesium neuroprotection, such as the annual number of publications, countries, institutions, authors, literature citations, and keywords.This analysis can provide a reference for researchers to grasp the research directions and hotspots comprehensively and accurately in neuroprotective effect of magnesium.

| Search strategy
The Web of Science Core Collection (WoSCC) was selected as the source database for data retrieval.We searched for relevant studies using the following strategy: TS-(neuroprotection OR neuroprotective) AND TS-(magnesium).The type of literature is limited to "article" or "review," the language is limited to English and the published time is limited between January 1, 1999, and August 1, 2023, and download in 1 day (August 1, 2023).Excluding publications: book chapter (n = 1), proceedings paper (n = 24), early access (n = 8), and retracted publication (n = 1).A total of 762 original English papers (included 570 articles and 192 reviews) were obtained.

| Countries/regions and institutions cooperation analysis
All published articles were from 216 institutions in 64 countries or regions.The co-occurrence analysis of cooperation network for countries or regions generated a total of 64 nodes and 59 links, with a density of 0.0293 (Figure 2A).As depicted in Table 1, the United States had the largest number of publications (269 publications, 27.12%), followed by China and Australia occupying the second and third place with 80 (8.06%) and 74 (7.46%) publications respectively.Ranked 4-10 are England, Canada, France, Germany, Turkey, New Zealand and the Netherlands.Among the top 10 countries in the number of publications, the top three countries in the mediated centrality were the Netherlands, England and the United States, indicating that the above countries played a constructive mediation role in the international cooperation in exploring magnesium of neuroprotection.
The institutional co-occurrence network map generated a total of 216 nodes and 358 links, with a density of 0.0154 (Figure 2B).The institution with the largest number of F I G U R E 1 Annual number of published articles from 1999 to 2023.

| Authors and co-cited authors analysis
The authors' co-occurrence network map generated a total of 261 nodes and 378 links with a density of 0.0111 (Figure 3), indicating

| Co-cited references analysis
References co-cited network map generated a total of 322 nodes and 363 links with a density of 0.007 (Figure 4).The larger the area of the node, the more times the literature has been cited.The literature marked by the purple circle had a higher centrality, which Review" entitled "Magnesium sulfate for women at risk of preterm birth for neuroprotection of the fetus" was the most cited article (39 citations) and had a high mediation centrality (0.78).Based on a systematic review of five clinical studies, this study found that prenatal magnesium sulfate treatment of women at risk of preterm birth significantly reduced the risk of cerebral palsy and the rate of substantial gross motor dysfunction in their children. 19The second most cited paper was a randomized controlled clinical study by Dwight J Rouse et al., which was published in "The New England Journal of Medicine" in 2008.This multicenter, placebo-controlled, doubleblind study enrolled 2241 women at risk for preterm birth between 24 and 31 weeks of gestation, and results showed a reduction in the incidence of moderate or severe cerebral palsy in surviving fetuses with magnesium administration. 20The first co-cited reference with the highest centrality was published in "The American Journal of Results of the analysis of 2589 patients with acute stroke showed that intravenous magnesium administration within 12 h after acute stroke did not significantly reduce the chance of death or disability. 22The fourth most cited study by Jeffrey L Saver et al. advanced the use of magnesium in the prehospital setting for acute stroke.
Of 1700 patients, 857 received magnesium injections and the rest received a placebo, which was initiated within 2 h of the onset of stroke symptoms.The results showed that prehospital treatment with magnesium sulfate was safe but did not improve clinical outcomes at 90 days in stroke patients. 23

| Keywords co-occurrence, clustering, timeline and burst analysis
The analysis of keywords can observe the dynamic research hotspots and trends in this field.The keyword co-occurrence map showed a total of 141 nodes, 163 links, with a density of 0.0165 (Figure 5A).The top 20 keywords with frequency are shown in The log-likelihood ratio algorithm was used to cluster keywords, and the feature labels were used to identify and rank each cluster to determine the research frontiers (Figure 5B).The overall module value of clustering Q = 0.772 (>0.3) indicated that the cluster structure was significant, and there was high heterogeneity among different clusters.
In the timeline diagram, keywords of the same cluster were arranged in chronological order of first appearance (Figure 6A

F I G U R E 5 Network diagram of keywords co-occurrence (A) and keywords cluster map (B).
bibliometric analysis, we provided a detailed review of the main research areas of the neuroprotective effects of magnesium, including magnesium therapy in perinatal, ischemic encephalopathy, subarachnoid hemorrhage, and emerging treatment modalities and strategies.

| Magnesium therapy for perinatal neural protection
Preterm birth is one of the most important causes of increased risk of perinatal neonatal death 24 and is associated with severe adverse neurological outcomes such as cerebral palsy, motor impairment, blindness, deafness, developmental delay, cognitive delay, poor academic performance, and behavioral disorders. 25According to the analysis of keywords emergence from CiteSpace, neural protective effect of magnesium in premature infants caused widespread attention since 2010, which might be related to several important clinical studies conducted and results published.The ACTOMgSO 4 trial by Caroline A Crowther et al. treated women at 30 weeks of gestation who were at risk for acute preterm birth with magnesium sulfate.Two years of follow-up results showed that substantial gross motor dysfunction, and combined death or substantial gross motor dysfunction were significantly reduced. 26In the study of French PREMAG, administration of magnesium sulfate to women with a gestational age of less than 33 weeks who were expected to deliver within 24 h resulted in a reduction in total fetal mortality and rates of severe white-matter injury. 27In BEAM trial, Magnesium treatment of women at risk for preterm birth between 24 and 31 weeks of gestation significantly reduced the frequency of moderate or severe fetal cerebral palsy. 20In the subsequent study, in which survivors from ACTOMgSO 4 and PREMAG trials participated in school-age followup, children in the magnesium group showed no significant differences in neurologic, cognitive, behavioral, growth, or functional outcomes from those in the control group, but superiority in the risk of death cannot be excluded. 28,29[32][33]

| Magnesium therapy for cerebral ischemic diseases
Cerebral ischemic disease is the most common cerebrovascular disease, and its high mortality and disability seriously damage human health.
The safety of magnesium therapy has been widely confirmed in premature infants, eclampsia, and neonatal hypoxic-ischemic encephalopathy, it has been gradually applied to the neuroprotective treatment of cerebral ischemic diseases.As shown in the CiteSpace analysis, from 1999 to 2008, the research of magnesium of cerebral ischemia received extensive attention.Animal studies have shown that intraperitoneal magnesium supplementation at 1 h or 30 min before ischemia can reduce the volume of cerebral infarction in rats with focal cerebral ischemia caused by middle cerebral artery occlusion. 12,34Moreover, intraperitoneal magnesium supplementation could improve the ischemic injury of global cerebral ischemia model by reducing the apoptosis of neurons. 35Studies indicated that serum magnesium concentration of 2.0-2.5 mmol/L had the best neuroprotective effect and intravenous magnesium supplementation further increased plasma magnesium concentration and reduced the influence of first-pass effect. 36Early magnesium treatment (within 2 h after ischemia) increased the survival rates, reduced the infarct volume and improved neurological function in rats with cerebral ischemia. 37,38Intraarterial magnesium supplementation rapidly increased the concentration of magnesium in the ischemic area and attenuated cardiac inhibition through the systemic circulation.
Pre-ischemia administration of magnesium sulfate through the carotid artery significantly reduced infarct volume in focal ischemia model rats. 39,40However, all these pathways were blocked by the blood-brain barrier, thus decreasing the concentration of magnesium entering the brain tissue.Subsequent trials of intracranial magnesium therapy discovered that parenchymal magnesium supplementation within 24 h after ischemia reduced nerve death in the ischemic brain region. 41,42sed on the promising effects in animal ischemic models, a series of clinical trials of magnesium as a neuroprotective agent in the treatment of cerebral ischemic diseases have been carried out (Table 6).The clinical studies had adequately confirmed the safety of magnesium but did not achieve significant improvement in clinical outcomes.In a substudy of IMAGES research, through the use of magnetic resonance imaging, with the growth of the cerebral infarction imaging results replacing the progression of clinical neurological symptoms, the therapeutic effect of magnesium was analyzed.The results demonstrated no significant differences in infarct growth between magnesium treatment group and placebo group, which was consistent with the clinical outcomes. 43Subgroup analysis of the IMAGES study suggested that magnesium might have an improved outcome in patients with lacunar infarction. 22A subsequent analysis of IMAGES data with adjustment for stratification variables provided further evidence of the positive effect of magnesium on lacunar infarction, however, further clinical studies were needed to confirm this finding. 44The negative results of these major clinical studies might explain the gradual decline in research heat on magnesium in ischemic cerebrovascular disease since 2013.Researchers hypothesized about possible reasons for negative results.In IMAGES study, mean duration of magnesium supplementation was 7 h, and only 3% was administered within 3 h after onset, which resulted in a decrease in volume of salvageable brain tissue, thus affecting clinical effect.In FAST-MAG trial, although mean duration of intravenous magnesium supplementation in prehospital setting was reduced to 45 min and serum magnesium concentration reached a threshold for a protective effect, it was unknown whether magnesium increase in brain tissue would have a beneficial effect.An exploratory analysis of ultra-early neurodegeneration in patients with acute cerebrovascular disease from FAST-MAG study showed that ultra-early neurological deterioration was significantly associated with poor outcomes and increased mortality. 45These results suggested that initiating stroke treatment as early as possible was advisable.Therefore, magnesium supplementation might still be administered early and achieve a brain-protective dose as soon as possible.

| Magnesium therapy for subarachnoid hemorrhage
Although results of CiteSpace analysis suggested that researches on magnesium therapy in subarachnoid hemorrhage gradually decreased after 2013, we still analyzed this field for the following reasons.One reason was that management of aneurysmal subarachnoid hemorrhage had improved considerably with development of surgery and endovascular treatment.7][48] Another reason was that magnesium had been studied as a pre-hospital emergency treatment for acute stroke, and subarachnoid hemorrhage is an important subtype of acute stroke; hence, magnesium neural protective effect of subarachnoid hemorrhage is worth further discussing.In rat model, intravenous magnesium supplementation reversed cerebral vasospasm TA B L E 5 Keywords cluster analysis.and reduced brain lesion volume in acute phase after subarachnoid hemorrhage. 49,50[53][54] The safety and efficacy of magnesium in treatment of vasospasm and delayed cerebral ischemia after subarachnoid hemorrhage was initially demonstrated in animal studies, series of clinical trials were subsequently conducted.Several small randomized clinical trials suggested that magnesium administration was safe after subarachnoid hemorrhage, and seemed to be effective in reducing delayed cerebral hemorrhage and improving poor prognosis.6][57][58][59] Contrary to expectations, IMASH trial involving 327 patients and MASH-2 trial involving 1024 patients demonstrated that intravenous magnesium sulfate therapy did not improve the clinical outcome of patients with subarachnoid hemorrhage. 60,61A metaanalysis of 13 trials collected analogous data in 2401 patients with subarachnoid hemorrhage found that prophylactic intravenous magnesium did not improve neurological outcomes or reduce cerebral infarction or mortality. 62One of the reasons for lack of effective clinical outcomes for magnesium might be delay in administration of the drug.In a meta-analysis, only 83 of 1965 patients were treated within 6 h, and small subgroups made it difficult to analyze the effect of dosing time windows on treatment effects. 63Moreover, cerebral vasospasm was not the only mechanism of delayed cerebral infarction, 64 and magnesium treatment alone might be arduous to achieve a desirable effect.Combination therapy of multiple mechanisms may be a promising solution.

| Magnesium combined with therapeutic hypothermia strategy
According to burst word analysis of CiteSpace, research on therapeutic hypothermia in neuroprotection of magnesium has attracted extensive attention since 2015.The neuroprotective mechanism of therapeutic hypothermia has been widely researched and affects physiological progress at multiple stages after cerebral ischemia.
It can play a regulatory role through multiple pathways such as apoptosis, excitotoxicity, inflammatory response, cell metabolism, blood-brain barrier, and blood flow. 65The neuroprotective effect of hypothermia on patients with cardiac arrest and neonatal hypoxicischemic encephalopathy has been confirmed, and both of them have been recommended as a feasible treatment by clinical practice guidelines. 66,67In recent years, clinical studies have combined local hypothermia with vascular recanalization therapy, which has been confirmed feasibly and safely in acute stroke. 68,69 a neuroprotective agent, magnesium has a synergistic effect when combined with therapeutic hypothermia, thus exerting a more powerful effect.In focal or global cerebral ischemia models, magnesium supplementation combined with hypothermia had a better neuroprotective effect than magnesium alone (Table 7).
It may also explain one of the reasons why effective results have not been achieved in clinical trials of magnesium treatment in stroke patients.Because clinical management of stroke requires maintenance of normal body temperature, which probably affects neuroprotective effect of magnesium.Although clinical studies of magnesium combined with hypothermia have not been conducted, the safety and efficacy of animal studies suggested that it is a promising clinical treatment strategy.In recent years, magnesium sulfate combined with therapeutic hypothermia in management of neonatal hypoxic-ischemic encephalopathy is being studied, and large-scale randomized controlled trials are still needed to further explore. 70,71

| Future therapeutic strategies for magnesium as neuroprotective agent
The neural protective effects of magnesium have been demonstrated in several animal models of cerebrovascular disease, and it has been recommended in clinical management of preterm infants with hypoxic-ischemic encephalopathy and cardiac arrest patients.
However, its clinical efficacy in stroke has not been proven.Future directions will focus on finding effective delivery routes, dosage forms, and combination treatment strategies for magnesium as a neuroprotective agent.
Both intravenous and intraarterial magnesium supplementation were hampered by the blood-brain barrier.Although studies had shown that BBB integrity was disrupted after stroke, an increase in BBB permeability was a stepwise process that required reduction in blood flow that lasted for several hours. 72The results of clinical studies suggested that magnesium supplementation as early as possible may improve clinical prognosis of stroke patients, and so intracranial magnesium may become a feasible administration route.Intracisternal magnesium sulfate has been attempted in subarachnoid hemorrhage, and results showed that it could reduce incidence of cerebral vasospasm and delayed cerebral ischemia and improve clinical outcomes. 73In cerebral ischemia, although routine surgery is not required, minimally invasive procedures can still be used to explore cisternal or intraventricular magnesium.
Although FAST-MAG trial, which explored magnesium as a pre-hospital emergency drug for acute stroke, did not achieve beneficial results, it provided a valuable evaluation and disposal method for magnesium application in pre-hospital treatment.than instillation of cold saline alone. 76Both magnesium and hypothermia can exert neuroprotective effects through multiple targets, which may partially explain their abilities to play a synergistic role.
The results suggested that local brain hypothermia combined with magnesium could provide neuroprotection during the critical early stages of cerebral ischemia, extend the time window for thrombolytic therapy, and help reduce the occurrence of reperfusion injury.
The concern is whether the injection of cold fluid into the local carotid artery affects hemodilution, which may lead to adverse consequences.However, clinical studies have found that the body can cope with rapid intravenous infusion of high-volume (>2000 mL/h) cold saline, and the fluid volume and infusion speed that required for local cerebral hypothermia to achieve the target temperature are much smaller than the maximum range. 77,78Thus, intra-carotid infusion of hypothermia magnesium solution after mechanical recanalization may be a new treatment strategy for patients with acute ischemic stroke who are eligible for endovascular treatment.

| LI M ITATI O N
To our knowledge, this is the first bibliometric study of articles in neuroprotective effect of magnesium using co-occurrence analysis and visual display of CiteSpace software.However, there are several limitations to our study.First, our study only included relevant articles published in the WoSCC database from 1999 to 2023, due to limitations of the software and the database itself.In addition, to facilitate analysis and generalization, we restricted the language to English and included only original articles and reviews to avoid duplication.Therefore, the data may not be comprehensive.We have also included articles outside restrictions for supplementary explanations in subsequent discussion section to elaborate on developments and trends in the field of magnesium neuroprotection as logically and clearly as possible.

| CON CLUS ION
This study uses an objective and quantitative method to explore the current status of magnesium neuroprotection in the past

3 . 1 |Figure 1 .
Figure 1.In the past 25 years, the number of publications on neuroprotective effect of magnesium has shown a dynamic upward trend.From 1999 to 2015, the number of published articles showed a slight increasement, and reached its peak in 2015, with 56 articles per year.From 2015 to 2023, the number of documents entered a relatively high level of stability, although with small fluctuations, indicating that the application of magnesium in neuroprotection has attracted more extensive attention.The number of articles published in 2022 reached 55, and although the data in 2023 is still incomplete, it is

SONG
et al.F I G U R E 2 Countries/regions (A) and institutions (B) co-occurrence network map.

| 5 of 19 SONG
et al. publications was the University of California System (33 publications, 3.02%), followed by the UDICE-French Research Universities (30 publications, 2.74%), the University of Adelaide (29 publications, 2.65%), the Institut National de la Sante et de la Recherche Medicale (Inserm) (29 publications, 2.65%) and the University of Texas System (26 publications, 2.38%).The United States National Institutes of Health had the highest mediated centrality of 0.39 and ranked seventh in the number of publications, indicating that it was in a crucial position in the cooperation and connection of institutions.
had important reference value and development significance in the research process of this field.The top 10 cited articles are shown in Table 3, with seven articles on neuroprotection in preterm infants and 3 in acute stroke.The effect of magnesium on fetuses at risk of preterm birth neuroprotection has always been a hot topic.The review published by Doyle LW et al. in the "Cochrane Database System Obstetrics and Gynecology" by Agustín Conde-Agudelo et al., which conducted a systematic review and meta-analysis and found that magnesium sulfate administered to women at risk of delivery before 34 weeks of gestation reduced the risk of fetal cerebral palsy21 Another important research direction is magnesium for neuroprotection in stroke.The third most cited article was published by K W Muir et al. in the Lancet in 2004.This randomized controlled trial known as the IMAGES study was one of the largest trials of a putative neuroprotective agent at the time and was well-designed.
), demonstrating the development of research on neural protective effects of magnesium.CiteSpace provides the burst detection function to explore large changes in citation to predict the migration and change of research frontiers.The top 20 keywords with the strongest citation bursts are shown in Figure 6B.From 1999 to 2008, magnesium treatment for traumatic brain injury, arterial occlusion, acute stroke, and subarachnoid hemorrhage attracted the attention of researchers.The main research methods were basic experiments in rats and intravenous magnesium, and the main directions were mechanism research including neurons, injury and infarct volume.Since 2010, more attention has been focused on magnesium in preterm birth, leading to a rapid development of the knowledge framework and clinical application in this field.At the same time, research on neuroprotection in ischemic encephalopathy was also ongoing but progress was relatively slow.In recent years, researchers have focused on the association between magnesium and neurological diseases such as ischemia, spinal cord injury, Alzheimer's disease, and the exploration of the combination of therapeutic hypothermia.These emerging keywords represented the future research trends and hotspots in this field.4 | DISCUSS ION Our study included relevant literatures in the field of magnesium neuroprotective effects from 1999 to 2023.Based on the above F I G U R E 4 References co-citation network map.TA B L E 3 Top 10 co-cited references.
It is worth thinking about how to combine convenience of drug administration with rapid achievement of effective doses.Oral high-permeability magnesium compound, currently known as magnesium L-threonine, has been shown to increase Mg + concentration in cerebrospinal fluid (CSF) in Parkinson's and Alzheimer's disease mouse models, with neuroprotective effects and cognitive function improvement. 74,75Its research value in cerebrovascular disease deserves further exploration.Limited by the time window of thrombolytic therapy, a considerable number of cerebral ischemia patients require endovascular treatment.Selective intra-arterial hypothermia after recanalization has a clinical benefit trend in patients with intracranial large vessel occlusion.In a rat model of transient middle cerebral artery occlusion, Wei Song et al. found that local intra-carotid instillation of cold magnesium sulfate was more efficient in reducing acute ischemic injury 25 years, which aims to provide researchers with a comprehensive and macro perspective to show the development trend of this field.Visual analysis demonstrated that this field of study is rapidly developing, with a consistent growth trend shown in the continually growing linked literature on the subject.The research focuses on preterm infant hypoxic encephalopathy, cerebrovascular disease, cognitive disorders and other neurological diseases.The neuroprotective effect of magnesium on preterm infants has been wellestablished and recommended by clinical guidelines.However, the clinical translations of magnesium in cerebral ischemia and subarachnoid hemorrhage are still problems that perplex researchers.The combination of magnesium and hypothermia has shown good potential and may become a development tendency and hot spot in the future.

TA B L E 1
Top 10 countries/regions and top 10 institutions with the most publications.

Table 4 .
The diseases or applications related to the neuroprotective effect of magnesium include cerebral palsy, preterm birth, brain injury, cerebral ischemia, traumatic brain injury, and subarachnoid hemorrhage.The research directions mainly included prevention, risk, blinding, controlled trial and treatment, and the hot research mechanism was oxidative stress.
TA B L E 4 Summary of clinical trials of magnesium in stroke.Neuroprotective effects of magnesium combined with hypothermia.
F I G U R E 6 Network diagram of keywords timelines (A) and top 20 keywords with the strongest citation bursts (B).TA B L E 6 TA B L E 7